docs: plan the est_tokens decoupling in five ordered tasks

The ordering is the load-bearing part. All three changes interlock and
every wrong interleaving fails silently: flipping the usage fallback to
(0, 0) before the settlement points read the derived value refunds the
whole pre-deduction on success, and flipping the embedding transport
before _merge goes three-state mislabels unavailable batches as
measured. So the plan adds the capability first, moves all five call
sites onto it while it is still equivalent, only then lets the third
state take effect, and unbinds the constraint last.

Registers both wiki entries and links the plan to its design.

research-wiki/graph/edges.json

@@ -105,6 +105,11 @@
       "id": "design:est-tokens-decoupling",
       "label": "est_tokens 解耦: 拆分限流预扣与遥测用量兜底(issue #2)",
       "type": "design"
+    },
+    {
+      "id": "plan:est-tokens-decoupling",
+      "label": "est_tokens 解耦实施计划",
+      "type": "plan"
     }
   ],
   "links": [
@@ -177,6 +182,13 @@
       "relation": "refines",
       "evidence": "精化 M1 冻结的 est_tokens 双职责语义: 保留 TPM 预扣、推翻 usage 缺失按 est 兜底(m1-core-design.md:59,222),改记 0/0 + unavailable + cost NULL",
       "added": "2026-07-30T09:33:55.383401+00:00"
+    },
+    {
+      "source": "plan:est-tokens-decoupling",
+      "target": "design:est-tokens-decoupling",
+      "relation": "implements",
+      "evidence": "5 任务实现设计 §3.2 的 11 条改动项;任务排序经中间态破窗分析(先加能力→切调用点→三态生效→解绑约束)",
+      "added": "2026-07-30T09:39:26.442986+00:00"
     }
   ]
 }